We propose to apply x-ray and neutron diffraction methods to study the molecular organization of the cholesteryl ester deposits of fatty streaks. This area will be approached by studies of human artery deposits and a comparison with pure lipid phases. The principal approaches follow: a) We will study the order-disorder transition of the droplets in slices of affected aorta using a thermally controlled polarizing microscope. We wish to establish the intra- and inter-cell distributions of transition temperatures. b) X-ray diffraction from single lesions will be used to compare lesions and establish the state of the lipids of a given lesion. c) Cholesteryl ester phases will be studied by x-ray and neutron diffraction in order to elucidate the molecular organizations of the smectic, cholesteric and liquid phases. d) If the correlation of the structures of the pure lipid phases with the atherosclerotic lesions is confirmed by comparison of data from a, b, and c, we will examine mixed phases of cholesteryl esters in an effort to reproduce the behavior of the lesion droplets in a model system.